The present invention relates to surveying instruments, whose actual readings, particularly the angle of elevation or horizontal direction azimuth, are subject to levelling errors when the instrument is erected and particularly to a theodolite having integrally connected apparatus for determining the levelling errors of the instrument and providing a corrective signal for error-compensation.
Various arrangements for stabilizing the spatial orientation of optical systems are known, as well as to compensate for the deviation from an ideal position. To stabilize entire instruments, it is known to mount them on a gyroscopic platform. The expense connected with this arrangement is a serious disadvantage. There has also been used means, for example, gyroscopes, spirit levels, pendulums and the like, as a reference for analyzing the rotary motion of an instrument. Thus the deviation of the instrument from its true level position can be automatically compensated by displacement of an optical element and/or the optical ray path. Such direct compensation results in extraordinarily large difficulties, particularly where incremental measuring methods are used, since instrumental vibrations result in ambiguities and averaging problems. In contrast to scale or code readings with a defined zero, incremental systems measure only directional variances by counting of individual or single steps during the movement from one direction to another. To modify the extent of such movement being defined by the aiming points by an amount corresponding to the error in horizontal orientation, cannot be successfully accomplished with the use of simple means.
The object of the present invention is, therefore, to provide surveying apparatus whose readings based on scale or code systems or for the incremental system can be faultlessly corrected with relatively low cost and at high satisfaction.
The foregoing objects, other objects as well as the numerous advantages of the present invention, are set forth in the following disclosure.